Heart rate variability (HRV) is a measure of the beat-to-beat variations in heart beat and it may be regarded as an indicator of the activity of autonomic regulation of circulatory function in response to an external or internal stimulation.
An analysis of HRV may find use in lie detection, which is generally performed based on body reactions not easily controlled by conscious mind, including, but not limited to, heart rate and skin conductivity. While the subject is asked a series of questions, lying will typically produce distinctive measurements of physiological responses of autonomic nervous system, due to emotional and psychological changes of the subject during questioning.